Physico-Chemical and Biological Evaluation of Spin-Coated Chromium-Doped Hydroxyapatite in Dextran Matrix Coatings

This study reports on the physico-chemical and in vitro biological characterization of chromium-doped hydroxyapatite (10CrHAp, Cr³⁺, Ca_10-xCr_x(PO₄)₆(OH)₂, x_Cr = 0.1) and chromium-doped hydroxyapatite in dextran matrix (10CrHAp-Dx) coatings, prepared for the first time via the spin coating technique. X-ray diffraction analysis and Rietveld refinement were used to characterize the materials. Fourier-transform infrared (FTIR) spectroscopy confirmed the presence of functional groups specific to hydroxyapatite. Scanning electron microscopy (SEM) observations revealed the presence of a conglomerate of nanoparticles distributed unevenly across the coatings surface. Atomic force microscopy (AFM) showed that both coatings presented continuous surfaces with uniform morphology. The in vitro biocompatibility of 10CrHAp and 10CrHAp-Dx coatings was evaluated using human osteoblast-like MG63 cell line and MTT assay. SEM and MM visualization assessed the cell adhesion and proliferation and morphological changes in the adhered cells. The antibacterial properties of the 10CrHAp and 10CrHAp-Dx coatings was assessed in vitro against two of the most common bacterial reference strains, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 25923. Overall, the coatings achieved log reductions up to ~9.35, corresponding to a bacterial kill rate (for S. aureus) exceeding 99.99%, with 10CrHAp-Dx showing slightly superior performance. Similar behavior (log reductions of ~8.6 and ~8.9, respectively, indicating a sustained antibacterial effect and >99.99% bacterial elimination) was observed and for Pseudomonas aeruginosa. AFM was used to evaluate the bacterial cells interaction with the coating's surfaces. The biological assays demonstrated that both coatings possess notable antibacterial activity, underscoring their potential in biomedical applications, particularly in the design of new antimicrobial devices.